1. Field of the Invention
The present invention relates to a display controller and, more particularly, to a display controller capable of producing multi-gradation images on a display device constructed by binary-state pixels in an array.
2. Description of the Related Art
Digitally commanded display devices usually refer to optoelectronic apparatus using a plurality of pixels as elementary light source units, in which each pixel is switched between binary states ON and OFF (or White and Black) under the control of digital electronic signals. As the elementary light source units, the pixels may be emissive, transmissive, and reflective types. Liquid display devices, light-emitting diode display devices, plasma display device, and the like are some examples of the digitally commanded display devices.
Since the binary-state pixels are limited to being operated at either the state ON or the state OFF, some kind of display techniques is necessarily utilized or developed in order to produce multi-gradation images on the display device consisting of the binary-state pixels (hereinafter referred to as a binary display device). For example, an analog modulation technique proposes providing the pixels of the binary display device with a plurality of driving signals, each of which has a different intermediate level of voltage, thereby possibly operating the pixels at several less than 100% ON/OFF states for achieving a display of multi-gradation. Such an analog modulation technique has a drawback of requiring a complicated driver.
Another prior art is a pulse width modulation technique for controlling duty cycles between the binary states ON and OFF and utilizing a low pass filtering function of the human eye to achieve a perception of multi-gradation. Such a pulse width modulation technique suffers from a complicated controller and a sophisticated controlling algorithm.
Alternatively, a prior art called frame rate modulation technique is proposed to produce a perception of multi-gradation through a display of consecutive frames. This prior art is similar in principle to the pulse width modulation technique. However, some undesired visual disturbance such as flickering is usually perceived in the displayed images.
Still another prior art is a dithering technique, which employs a dither matrix to eliminate the flickering of the displayed images. However, such a dithering technique requires a sophisticated controlling algorithm and circuitry, resulting a low utility ratio of digital information. Even worse, some undesired visual disturbance such as stripes might be perceived in the displayed image.